A grain-oriented electrical steel sheets and a non-oriented electrical steel sheet are widely used as core materials for various transformers, electric machineries, power generators and the like. Among them, the grain-oriented electrical steel sheet is featured to have good iron loss properties directly leading to reduction of energy loss in the transformer, power generator or the like that the magnetic flux density is high and the iron loss is low because crystal orientation is highly accumulated in {110}<001> orientation called Goss orientation.
When the core of the small-sized power generator or the small-sized electric machinery, the EI core or the like is manufactured by using such a grain-oriented electrical steel sheet, punching or shearing is frequently conducted after the leveling for correcting a coil form. In the leveling, punching or shearing, however, twining deformation is caused in the steel sheet to generate cracking, chipping or warping, whereby production troubles may be caused. Even in the production of the wound core, twin is generated when the steel sheet is wound in the form of a coil, whereby magnetic properties may be deteriorated.
To this end, there are proposed various techniques for improving workability. For example, Patent Document 1 proposes a technique of suppressing the generation of twin by reducing S and N among ingredients of a raw material and adding SO3 compound to an annealing separator in an amount of 0.5˜5.0 mass % as SO3 weight. Also, Patent Document 2 proposes a technique of preventing the cracking in the shearing or bending by restricting Ti concentration in the steel sheet inclusive of forsterite film to a range of 1.0˜2.0 times of N concentration to reduce N in steel.